DESCRIPTION (adapted from the application) This application for an RO3 is to serve as a supplement to K08 DK02635&#8209;03. The title of the original K08 is "Growth and Death Signals in the Prostate". As a gastroenterologist, my clinical and research focus is inflammatory bowel disease. Specifically, I am interested in intestinal epithelial cell apoptosis and its role in barrier dysfunction in the inflamed intestine. Because of that interest, I chose Dr. Charles Sawyers as my mentor for the K08. Although seemingly disparate systems, the research in Dr. Sawyers' laboratory on prostate cell apoptosis has given me the tools to transition back to the intestinal tract and further an understanding of intestinal epithelial cell apoptosis as it relates to inflammation. The experimental strategies described in this proposal build upon my post&#8209;doctoral experience in the laboratory of Dr. Sawyers utilizing genetic strategies to define signaling pathways and my experience in studying intestinal epithelial cell apoptosis and its effects on barrier function. During the initial two years of the K08, I completed a study examining the role of MEKK1 in androgen receptor signaling and described an important, previously unknown interplay between the MEKK pathway and androgen receptor transcriptional regulation (Abreu&#8209;Martin et al. 1999). I have also developed a model of Fas&#8209;mediated apoptosis and its effect on intestinal barrier function (Abreu et al. 2000). The results of our studies suggest that the intestinal epithelium is quite resilient in the face of immune-mediated apoptosis because the remaining epithelial cells dramatically restructure their tight junctions and maintain E-cadherin-mediated cell contact to prevent holes in the monolayer. I am now poised to merge these two areas of research in this proposal entitled PI3'-kinase-dependent protection from Fas-mediated apoptosis in the gut: role in maintenance of barrier function." We will test the hypothesis that PI3'-kinase-dependent mechanisms protect intestinal epithelial cells from Fas-mediated apoptosis and barrier dysfunction. Preliminary data demonstrates [sic] that inhibition of PI3'-kinase dramatically sensitizes intestinal epithelial cells to Fas-mediated apoptosis and barrier dysfunction. Expression of constitutively-active Akt, an important kinase downstream of PI3'-kinase, protects against Fas-mediated apoptosis. Moreover, cross-linking of Fas leads to phosphorylation of Akt suggesting activation of a survival pathway in addition to a death pathway. Our specific aims will trace the protective effect of PI3'-kinase from the plasma membrane to the nucleus. The results of this study have implications for the medical therapy of inflammatory bowel disease. These diseases are manifested by immune-mediated destruction of the lining intestinal epithelial cells. The support from this R03 will permit me to successfully compete for an R01 and make the transition to an independent investigator.